300SD Climate Control

I just bought a '83 300SD and I'm having a little trouble with the climate control. When I put the heat on it blows warm in the front but the vent at the back of the console continually blows cold.

Am I doing something wrong?

[Robert W. Roe]

There is a lever on the rear vent that I slid all the way to the right. This turns off the cold air coming out here. In the summer, I might open it, if it's blowing cold air-conditioned air. If I was really worried about it, I might get the servos checked, but the system works.

Also, I get a fairly wide variation in temperature of the air that comes from the dash vents. Once on a long trip last winter it annoyed me enough that I turned the fan to "low" once the interior got nice and warm.

I think that the climate controls are a weak spot in these cars, but if it can be adjusted to give you heat and cool air as appropriate in the correct amounts, it's working.

The whole climate control system, to me anyway, is a bit mysterious. At least the system doesn't have to be constantly adjusted; the automatic temperature setting is cool.

[mbdoc]

AS Robert stated the rear vent allows only cold/fresh out. Many times the lever doesn't shut the air completely off. IT can be adjusted.
One of the most important items for the A/C/C system to operate correctly is the in-car temp sensor, air has be be drawn across this sensor. MB used a foam rubber hose & they fall apart after 5-6 years. Without air flow across this sensor the system operates slowly. Cars after 84-85(depends on model) used a electric motor to aspirate the sensor. At dealer we retro-fitted this motor to the 1985 W126 chassis. I have installed this set-up on many cars so that system can operate & give EVEN heating/cooling. When the sensor was moved to the roof area the systems worked much better.

[bbeardb]

Originally Posted by M.B.DOC

AS Robert stated the rear vent allows only cold/fresh out.

This is from way back, but is this true? My rear vent only blows cool air and I'm sure they designed it to blow whatever air is blowing out the rest of the vents. My side window defogging vents (but not the ones below it) don't seem to move much air. I'm wondering if they are related. Evertything else seems to work just fine.

I'm sure "closing the vent" is a solution to blowing cold air, but not a solution to get it to blow warm if (that is, if it is designed to.)

Thanks,

[Brian Carlton]

Originally Posted by bbeardb

This is from way back, but is this true? My rear vent only blows cool air and I'm sure they designed it to blow whatever air is blowing out the rest of the vents.

I'm quite confident that you can believe whatever M.B.Doc tells you.

[engatwork]

but is this true

I'm with Brian on this. If M.B. Doc says it you can take it to the bank.

[SD Blue]

My understanding of the W126 and the diagrams. Someone correct me if I am wrong. Cool/Fresh air is all that is available from the center rear vent. Rear heat is ducted to the feet only (there is a duct system that runs under the front seats).

If the control lever at the rear center vent doesn't shut the cool air off, then more than likely a clamp has popped loose from one end and the cable jacket is not anchored. The other end of that cable can be seen by pulling the glove box and looking at the right side of the center plenum with a flashlight. (I just had mine apart a couple of weeks ago for a pod repair.) Who knows you may be able to fix it with minor disassembly!

[Pete Burton]

yep, non-heated air only to the rear center vent. The owner's manual states this too. If you pop the ashtray + money tray assy out you can see (and reach) where the front end of the cable wire attaches. The sheath is held by a spring clip. SD Blue, I have my center console out right now. Any sage advice about checking/replacing that center pod would be greatly appreciated. I figure I should do it now.

[SD Blue]

If I recall DMorrison has some photos of this but I don't recall how long ago.

To remove it you will need to pull the ACC controller and center vents. Also, removing the glove box liner is good spot for some light. It is a good idea to plug the lower area with some rags or something because parts can disappear into the great black hole.

Remove a couple of the plugs and the rubber flex ducting away from the right side of the center vents. To remove the pod itself, there is a small portion of the plenum that is attached with very small screws behind it. Once they are removed,(long 1/4 dr. wobble ext.) you can pull the pod and mounting out enough to see the actuator rod. Push the rod to the left and it should pop out of the clip. (this clip is the same type as the one on the top right side of the plenum for the defrost actuator rod)

Once you've rebuilt the pod, I found that some light wire, looped through a small hole on the flap, and some hemostats held the flap down in order to reinsert the actuator rod.

It is a bear because you have to see what you are doing, insert several tools and work in an area about the size of a wall outlet.

[aroohk]

I am in the process of figuring out why my rear seat vent does not blow at all, and was wondering if anyone had an exploded diagram of that area! Any help would be appreciated as I am hoping to tear into this over the weekend!

Sincerely,
Aaron

[BenzGeek]

my husband has been working on the climate control in my 300d for a bit and is trying to figure out where everything is under the dash. we were wondering if there happened to be someplace here that had a diagram of the duct system that included switches/valves. we are both a bit clueless as to what we are looking at. this thread seems very helpful, though, so i figured since y'all were on the topic of ducts, maybe you would also know where to find a diagram of what's all involved in the climate control, if one existed at all.

thank you for any help you can give!